The present invention relates to a means for elimination for frequency control of health injurious noise originating in high frequency oscillations in cutting tools, and in particular tool adaptors for eliminating such noise.
Vibrations in cutting tools most often will result in unacceptable surfaces, and/or deviations in geometry and dimensions of the work piece. Vibrations may also easily lead to mechanical overload and damage to machines and tools. In addition, the vibrations often will excite noise which is troublesome or even damaging to health within the work area of the machine operator.
In some unique cases, noise is the only noticeable disadvantage of the vibrations in the cutting tool. Ejector boring may be the most typical machining process where this is often the case; however also in short hole boring, lathe cutting and other operations there will often be vibrations to give unhealthy noise, without having unacceptable machining results. Traditionally the situation has been that proper quality and optimum productivity have impelled the development of tools, while the motivation for working with pure noise suppression in chip cutting operations, has so far not been particularly great.
Laws and regulations relating to the work environment, have been made more stringent internationally, and this has had as a result that health injurious noise burdens in the work areas of the operators are no longer acceptable, and the engineering industry has become busy finding solutions.
The present invention is a solution which will remove a large part of the applications which suddenly now have landed on the engineering industry's list of unacceptable sources of noise.
Even if the prior art so far regarding damping vibrations in cutting operations originate in a motivation for improving processes where vibrations are a quality-related or a productivity-hampering problem. It is also naturally a fact that all damping of vibrations is also suppression of noise.
U.S. Pat. No. 3,663,116 shows an arrangement intended to dampen torsional vibrations in machine parts which can be regarded as cantilever beams, in particular tool holders which are clamped tightly in one end, such as boring bars. The arrangement consists of an outer jacket, which in one end is fixedly connected to a torsionally stiff core which is situated centrally within the jacket. An energy dissipating material between the inner jacket surface and the outer surface of the core, provides for damping of torsional movements between the jacket and the core. A special feature of this arrangement is that the jacket itself will always have to be deformed more than the energy-absorbing material during such torsional motion.
U.S. Pat. No. 4,447,181 shows an arrangement intended to dampen vibrations and clattering in a tool holder, by means of a recess provided in the center of the engagement surface between the tool holder and the further fastening means therefor toward the tool machine, inside which recess a rubber pad is compressed.
U.S. Pat. No. 4,491,044 discloses an arrangement for damping a tool fixing plate for several boring bars, mounted on a revolver in a tool machine, and in which the clearance between tool surfaces and hydraulic seals create a closed damping chamber between the revolver spindle end surface and the tool fixing plate. Oil or a viscoelastic material in the damping chamber is intended to dampen the relative movement between the fixing plate and the revolver.
U.S. Pat. No. 5,033,340 discloses an arrangement intended to minimize high frequency vibrations of a boring bar cutting tip, by compressing a damping sandwich placed at a joint between the boring bar holder and the tool mounting area of the tool machine. An essential part of the arrangement is how to fix the holder against the mount area while avoiding metal-to-metal contact in the compression direction of the damping sandwich.
As to conception, the present invention differs from all the above mentioned arrangements in that it comes as a solution to a problem which is exclusively a work environmental problem, and not a quality or productivity problem. The primary value is the user's experience of the invention as a noise suppression means, and this experience is the most important motivation for its conception.
Technically, the present invention differs from all the above mentioned arrangements in that it is based upon the feature that possible oscillations in the tool must first be guided into a simple oscillation which will not give any negative results in the machined work piece, and that thereafter, sufficient energy is taken out of the oscillation that it does not excite any troublesome sound in the machining process.
The present invention is primarily intended to be utilized in tool mount adaptors with a standard interface, which can be inserted in the tool machine as a modular tool adaptor. As an alternative to reductions in cutting speed, efficiency-diminishing design changes in the tool itself, or noise-isolating cabinets built around the complete tool machine, such an adaptor will have a superior utilitarian value.
For boring tools, the utilization of the invention is relatively simple. In this case one will often find that the noise-generating oscillations substantially coincide with pure torsional oscillations in the tool. This oscillation has the effect that the cutting speed of the edges varies; however it does not affect measurably the produced quality, neither in diameter nor in the surface. Such oscillations can also be advantageous for the progress of the cutting operation in that they pulse the laminating process, and thereby ensures chip breaking in the machining.
The adaptor in accordance with the invention is defined precisely in the appended patent claims.